1. Field of the Invention
The present invention relates to a control circuit for setting a .DELTA.Vbe/R bias source at partial stand-by by a stand-by control signal.
This application is related to an application entitled DEVICE FOR SETTING A BIAS SOURCE AT STAND-BY and to an application entitled BIAS SOURCE CONTROL CIRCUIT, both filed on an even date herewith, and incorporated herein by reference.
2. Discussion of the Related Art
Stand-by circuits are used to reduce power consumption in a circuit during periods of non-use by deactivating the bias source, without it being necessary to switch off the circuit. They are of particular interest for systems with an independent power supply, consisting of, for example, ordinary or rechargeable batteries, such as remote sensors. The role of such sensors is, for example, to transmit data to a control panel in the case of a change in the state of the sensor. In such devices, it is essential to limit the consumption of the sensor during periods when its state is stable. In order to do this, the bias source of its emission units is set at stand-by when the sensor is in a stable state for a predetermined time interval. This enables the consumption of the device to be reduced during these periods. The bias source is reactivated as soon as the stand-by control signal changes state, giving an indication that the sensor no longer is in a stable state.
A disadvantage of conventional stand-by circuits lies in their power consumption during their switching and during the bias source stand-by periods. In fact, for the purposes of stand-by control, in general, a logic device based on inverters is used. The role of this device is to transform the stand-by control signal into a logic signal from the viewpoint of the bias source. The current consumption of the inverter has, when switching, a peak value which is damped through the series resistors of the MOS transistors which constitute the inverter. This power consumption is therefore a function of the switching time of the stand-by control signal.
Moreover, although the stand-by signal is in general already a logic signal, often the potentials of its states do not correspond to the supply potentials of the bias source. Thereby a continuous level of residual power is consumed during the stand-by periods of the bias source. This power consumption increases as the difference between the low state of the stand-by control signal and the potential of the negative power supply terminal of the bias source increases.
In addition, in some cases, it is required that certain circuit units be activated by the bias source, while other units could be set at stand-by.
The current solution to this type of situation is to provide a distinct bias source for each unit, or group of units of the circuit that can be set at stand-by at the same time. Thus, in order to reduce the power consumption of the circuit, the number of bias sources must necessarily be increased, which increases the surface area of the chip needed to implement the circuit in the form of an integrated circuit.